Github user wzhfy commented on the issue:
https://github.com/apache/spark/pull/15637
For equi-height hsitogram, we need extra info like ndv's in each bin. Does
count min sketch also have this information? I had a discussion with Herman and
Tim about histogram construction before, we want to compute all stats including
histograms in a single table scan. They suggested we modify
ApproximatePercentile to get equi-height histograms, i.e. endpoints of bins and
the ndv's within them. And this pr is only for getting equi-width histograms.
You can check [this JIRA](https://issues.apache.org/jira/browse/SPARK-17074)
for the discussion.
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